Java设计模式研究之Flyweight模式
2008-01-05 09:44:10 来源:WEB开发网核心提示:GOF:运用共享技术有效地支持大量细粒度的对象, 解释一下概念:也就是说在一个系统中假如有多个相同的对象,Java设计模式研究之Flyweight模式,那么只共享一份就可以了,不必每个都去实例化一个对象,此时变量flyweight为null,产生一个新的flyweight存储在Hashtable中,比如说(这里引用GO
GOF:运用共享技术有效地支持大量细粒度的对象。
解释一下概念:也就是说在一个系统中假如有多个相同的对象,那么只共享一份就可以了,不必每个都去实例化一个对象。比如说(这里引用GOF书中的例子)一个文本系统,每个字母定一个对象,那么大小写字母一共就是52个,那么就要定义52个对象。假如有一个1M的文本,那么字母是何其的多,假如每个字母都定义一个对象那么内存早就爆了。那么假如要是每个字母都共享一个对象,那么就大大节约了资源。
在Flyweight模式中,由于要产生各种各样的对象,所以在Flyweight(享元)模式中常出现Factory模式。Flyweight的内部状态是用来共享的,Flyweight factory负责维护一个对象存储池(Flyweight Pool)来存放内部状态的对象。Flyweight模式是一个提高程序效率和性能的模式,会大大加快程序的运行速度.应用场合很多,下面举个例子:
先定义一个抽象的Flyweight类:
package Flyweight;
public abstract class Flyweight
...
{
public abstract void Operation();
}//end abstract class Flyweight
在实现一个具体类:
package Flyweight;
public class ConcreteFlyweight extends Flyweight
...
{
PRivate String string;
public ConcreteFlyweight(String str)
...
{
string = str;
}//end ConcreteFlyweight(...)
public void operation()
...
{
System.out.println("Concrete---Flyweight : " + string);
}//end operation()
}//end class ConcreteFlyweight
实现一个工厂方法类:
package Flyweight;
import java.util.Hashtable;
public class FlyweightFactory
...
{
private Hashtable flyweights = new Hashtable();//----------------------------1
public FlyweightFactory() ...{}
public Flyweight getFlyWeight(Object obj)
...
{
Flyweight flyweight = (Flyweight) flyweights.get(obj);//----------------2
if(flyweight == null) ...{//---------------------------------------------------3
//产生新的ConcreteFlyweight
flyweight = new ConcreteFlyweight((String)obj);
flyweights.put(obj, flyweight);//--------------------------------------5
}
return flyweight;//---------------------------------------------------------6
}//end GetFlyWeight(...)
public int getFlyweightSize()
...
{
return flyweights.size();
}
}//end class FlyweightFactory
这个工厂方法类非常要害,这里具体解释一下:
在1处定义了一个Hashtable用来存储各个对象;在2处选出要实例化的对象,在6处将该对象返回,假如在Hashtable中没有要选择的对象,此时变量flyweight为null,产生一个新的flyweight存储在Hashtable中,并将该对象返回。
最后看看Flyweight的调用:
package Flyweight;
import java.util.Hashtable;
public class FlyweightPattern ...{
FlyweightFactory factory = new FlyweightFactory();
Flyweight fly1;
Flyweight fly2;
Flyweight fly3;
Flyweight fly4;
Flyweight fly5;
Flyweight fly6;
/** *//** Creates a new instance of FlyweightPattern */
public FlyweightPattern() ...{
fly1 = factory.getFlyWeight("Google");
fly2 = factory.getFlyWeight("Qutr");
fly3 = factory.getFlyWeight("Google");
fly4 = factory.getFlyWeight("Google");
fly5 = factory.getFlyWeight("Google");
fly6 = factory.getFlyWeight("Google");
}//end FlyweightPattern()
public void showFlyweight()
...
{
fly1.operation();
fly2.operation();
fly3.operation();
fly4.operation();
fly5.operation();
fly6.operation();
int objSize = factory.getFlyweightSize();
System.out.println("objSize = " + objSize);
}//end showFlyweight()
public static void main(String[] args)
...
{
System.out.println("The FlyWeight Pattern!");
FlyweightPattern fp = new FlyweightPattern();
fp.showFlyweight();
}//end main(...)
}//end class FlyweightPattern
下面是运行结果:
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